Heaters are used in many applications where heat is required to help warm an adjacent area. Electrothermal deicing is a common way to protect airfoil surfaces from ice accumulation, that is by providing heaters bonded to or integrated within the structure to remove or eliminate ice build-up. It is used wherever icing conditions exist, including applications such as, but not limited to, airfoil leading edges of wings, tails, propellers, helicopter rotor blades, engine inlets, ships, towers, wind turbine blades, and the like, for example. It may also be used in internal areas of an aircraft, examples in areas such as the cockpit cabin or floors for warming, or pipes that may contain liquids that could freeze. In electrothermal deicing systems, heat energy is typically applied to the airfoil surface through a metallic heating element via electrical power supplied by aircraft or appropriate application generators. Typical heating elements are made from foil, wire and metallic-coated fabrics.
Generally, the heating element of an electrothermal deicer should be highly flexible to conform to many types of surface areas and shapes to be ice protected. Such surface areas may be either two- or three-dimensional. In addition, such heating elements should also withstand fatigue and foreign object damage (FOD) requirements for each particular application. Further, such heating elements should be capable of being specifically designed to provide exact power levels (heat) and uniform heat distribution to the protected surfaces which may vary over the airfoil. This allows removal of ice or the prevention of ice while minimizing the power requirements of the electrothermal deicer.
The prior art includes a movable sheet having a rectangular array of perforations and mounted on rollers, as disclosed in U.S. Pat. No. 5,590,854; a grid-type of electrical heating element that is painted on, as disclosed in U.S. Pat. No. 6,027,075, and a mesh of interwoven wire, as disclosed in U.S. Pat. No. 6,832,742. However, most current heater elements are made from a single channel foil or wire element assembly as exemplified by the illustrations of FIGS. 6 and 7, respectively. Accordingly, a failure of a single ribbon via FOD/fatigue in most current heater elements can reduce or eliminate the heating element's usefulness.